Alloy process



Patented Apr. 5, 1949 ALLOY raoonss Alexander L. Feild, Baltimore, Md.,asslgnor, by

mesne assignments, to Armco Steel Corporation, a corporation of Ohio NoDrawing.

Original application March 19,

1941, Serial No. 384,206. Divided and this application May 26, 1945,Serial'No. 596,077

3. Claims. 1

This application is a division of my copend-ing application Serial No.384,206, filed March 19, 1941, now Patent No, 2,378,397, entitled Alloyprocess and the invention relates to the art of producing the same.

One object of my invention is the provision of a processfor producingnitrogen-containing iron-chromium alloys which is simple to perform,requiring little time and labor, and which makes use of an inexpensiveand available nitrogen --bearing material.

Another object is to provide a process for \producingnitrogen-containing stainless steel, which is economically practiced,which is highly efiective in character, which can be employed usingaclean and inexpensive nitrogen-containing material which keeps well andis convenientl and easily stored and which is easy to use in conjunc-:tion with operations now employed in producing stainless steel.

A further object of my invention is that of pro viding a process forintroducing nitrogen into stainless steel; the employ ent of whichenables. the production in a simple, direct manner of stainless steel offine even grain which is clean, sound, strong, durable, heat-resistantand cor-- rosion-resistant; which possesses high tensile strength, andhigh impact value; that lends itself to hot and cold working, hardening,polishing, and the like; and which is highly resistant todecarburization and grain growth under the many conditions offabrication and use,

Other objects in part will be obvious and in part pointed outhereinafter.

The invention, accordingly consists in the combination of elements,composition of ingredients, and mixture of materials, and in the severalsteps and in the relation of each of the same to one or more of theothers as described herein, the scope of the application of which isindicated in the following claims.

As conducive to a clearer understanding of my invention, it may be notedat this point that stainless steel is a low-carbon alloy of iron andchromium, which usually contains some to chromium, with 01' withoutnickel; and for special purposes supplementary additions of manganese,copper, silicon, tungsten, molybdenum, vanadium, titanium, columbium,tellurium, selenium, sulphur, phosphorus and the like.Nitrogen-containing stainless steel possesses many improvedcharacteristics as compared with ordinary stainless steel. The effect ofnitrogen upon stainless steel differs depending upon the grade of thesteeL- For example, Patent No.

2,118,693 to Arness, issued May 24, 1938, discloses nitrogen-treatedstainless steel of the ferritic iron chromium grade comprising 10% to30% chromium, 0.06% to 0.30% carbon and 0.06% to 0.20% nitrogen.Nitrogen, here, lends refinement to the metal grain structure and makesthe metal more resistant to decarburization and grain growth infabrication and use. Such alloy products are more ductile, moreworkable, and lend themselves more readily to hardening by heattreatment over a wider range of chromium content. tensile strength, andcold forming operations can be carried out upon them over a wider range.of temperatures.

A nitrogen-containing austenitic-iron chr0- mium nickel alloy isdisclosed in the Arness P-atent 2,121,391, issued June 21, 1938.Nitrogen improves the work hardening characteristics of a stainlesssteel of the austenitic grade. Cold worked products formedfrom suchsteel are much superior, in elastic limit and in ductility, to ordinaryaustenitic-iron chromium nickel steel products.

The properties conveyed by the nitrogen content of non-corrosive ferrousalloys are in some respects similar to the well-known propertiesresulting from the use of a small increased amount of carbon without,however, the accompanying undesirable effects of carbon on corrosionresistance and without decarburization and surface grain growth. Aparticular added amount of nitrogen must be present in stainless steelto lend improvement to certain qualities of the steel. Or-

dinarily a bath of stainless steel absorbs up to 0.03% nitrogen from thesurrounding atmosphere. Usually a nitrogen-containing material is addedto the bath in such quantities that the finished metal analyzes some0.06% to 0.20% nitrogen. Care must be exercised to avoid the absorptionof too much nitrogen, otherwise the metal will be defective, unsound andbrittle.

Prior processes for introducing nitrogen into non-corrosive ferrousalloys have p oven to be expensive in practice or, in other respects,not completely satisfactory. The nitrogen-containing treating materialsemployed in these processes are, for example, expensive or difiicult toprocure, or costly to prepare. Moreover, such materials often arediflicult to handle without great waste, while others contain certainimpuri ties which affect the metal detrimentally. Still othernitrogen-containing materials are objectionable for, following theiruse, traces of certain elements inconsistent with particular alloyspeci- The products are of materially improved gen unless such materialsare used in large quan-:

titles. There are, therefore, many important points to be consideredwhen a nitrogen-containing material is chosen for use inintroducingnitrogen into stainless steel.

Accordingly, an object of my invention is the provision of a new processand material for introducing nitrogen into non-corrosive ferrous alloys,which enables the cheap production of nitrogen-containing stainlesssteel, which gives a 0d, such as by compressing it, using some suitablebonding material. with or without the addition of a weighting materialsuch as steel turnings or filings. I find that my nitrogen-containingmaterial can be mixed and compressed with any solid material that isadded to a stainless steel bath during the processing of the steel. Asan example, I mix and compress together quantities of ferrousferricyanide, pulverized low-carbon ferrochrome and a suitable bondingmaterial. As more specifically set out hereinafter, the chromium andnitrogen contents of'a stainless steel bath are increased when mymixture of ferrochrome and metal product uniformly containing the properamount of nitrogen, which enables nitrogen to be introduced into anon-corrosive alloy without the addition of carbon in excessive amountsor of any other objectionable impurity or material which is inconsistentwith the alloy metal specifications, and which in use cause a highpercentage of available nitrogen to be released into the alloy metalwith highly effective and benefi'cial results. 7 Referring now moreparticularly to the prac tice of my invention, I introduce nitrogen intoa non-corrosive ferrous alloy during its production by way of ferrousferricyanide Fe3(Fe(CN) (5)2, more commonly identified by the tradename, Prussian Blue or Turnbulls Blue. Ferrous ferrie cyanide comprisesa plentiful amount of nitrogen. Thi nitrogen is released readily whenthe nitrogen-containing material is brought in contact with a bath ofstainless steel. In its pure state, ferrous ferricyanide contains about28% nitrogen, the balance being carbon and metallic iron. Thecomposition of commercial ferrous ferricyanide does not differconsiderably from the composition of the compound in its pure state.

I find that around 50% of the nitrogen available in mynitrogen-containing material is picked up by a stainless steel bath.Therefore, since ferrous ferricyanide so effectively lends nitrogen to ametal bath, only small amounts of the material need be used toaccomplish good results. Further, once the amount of nitrogen which isto be introduced into a metal bath is known, it is but a simple matterto place suflicient quantities of ferrous ferricyanide in the moltenmetal to release the determined amount of nitrogen. The

amount of nitrogen which ferrous ferricyanide yields to a particulargrade of stainless steel can be ascertained by experiment. Thereafter,the

amount of the nitrogen-containing material needed to impart a certainquantity of nitrogen to that particular stainless steel can be basedupon previously recorded experimental data.

Ferrous ferricyanide is available commercially in large quantities andat relatively low cost by comparison with heretofore usednitrogen-containing materials.

Dried ferrous ferricyanide, as purchased on the market, is an almostimpalpable powder. Thus, when the powdered material is placed on thesurface of a stainless steel bath, difficulty is encountered in gettingthe powder to sink into and mix with the metal. Accordingly, I prefer toimcrease the density of the material in any convenient and practicalmanner causing it to sink, mix

and give off nitrogen more readily in a bath of stainless steel. Forexample, I prefer to briquette the ferrous ferricyanide by any wellknown meth--.

ferrous ferricyanide is added to the metal.

As illustrative of the practice of my invention, a heat of stainlesssteel :is produced in any well known manner, for example, by usingstainless steel scrap and high-carbon ferrochrome as sources ofchromium, as disclosed in the Patent No. 1,925,182 to Feild, issuedSeptember 5, 1933; or in accordance with the method described andclaimed in the Arness Patent No. 1,954,400, issued April 10, 1934,wherein rustless iron scrap and chromium ore are used as the principalsources of chromium; or in accordance with the method described andclaimed in the Arness Patent No. 2,056,162, issued October 6, 1936,wherein rustless iron scrap, high-carbon ferrochrome and chrome ore areused.

I make up a finishing slag on the metal bath,- employing such materialsas ferro-silicon and ferro-manganese. As desired, along withferrosilicon and ferro-manganese, ferrochrome is added in amountssufncient to adjust the chromium content of the bath. I also add aproper quantity of briquettes containing ferrous ferri-,

cyanide to the metal bath which are decomposed therein. Nitrogen isreleased by the de-.- composing briquettes, the nitrogen beingquicklyassimilated throughout the metal and beingab sorbed quite readilyby the metal. Thereafter, I tap the metal into a ladle from which it isteemed. into suitable ingot molds where it is permitted to. solidify andcool. The molds are then stripped from the ingots and the ingots storedand converted into various semi-finished products as desired. Instead ofadding ferrous ferricyanide briquettes of the type described above tothe metal bath, I obtain .very good nitrogen-containing stainless steelby using briquettes comprising amixture of pulverized low-carbonferrochrome and ferrous ferricyanide. The chromium and nitrogen presentin the bath are brought up to:- specifications by dropping a sufficientnumber of these briquettes into the bath during the finishing operation.It is well known that chromium has a great thirst for nitrogen. Much ofthe nitrogen released by ferrous ferricyanide in the briquettes, as theydecompose in the bath, is absorbed im-,.- mediately by the chromiumderived from the ferrcchrome briquette constituent. Nitrogen absorption,therefore, i very complete since the? nitrogen is in immediate contactwith an abun-- dance of chromium. The added chromium, and the nitrogenwhich it absorbs, are distributed uniformly throughout the metal bathduring the processing operation. As before, the finished metal is tappedinto a ladle and teemed into ingot molds to solidify and cool.

At .times I find it advantageous to introduce. ferrous ferricyanide intostainless steel before the: furnace finishing stage is reached, orduring, or after the tapping of the melt into a ladle following the.furnace finishing stage. Generally, the;

amount of carbon which the metal picks up from ferrous ferricyanide isnot objectionable. When, however, the production of extremely lowcarbon, nitrogen-containing stainless steel is sought, the ferrousferricyanide is introduced during early furnacing stages and much of thecarbon is eliminated from the melt before the finishing stage isreached. Further, I find that an excellent distribution of nitrogenthroughout the metal is obtained when my nitrogen-containing material isadded to the molten metal in the ladle. This is done by shoveling aquantity of powdered or briquetted ferrous ferricyanide into the ladleduring the metal tappin operation. The turbulent action of the metal, asit pours into the ladle, effects a stirring action. This action ishighly effective in distributing nitrogen given off by thenitrogen-containing material very completely throughout the metal.

A 13-ton heat of 17% chromium grade stainless steel picks up about 50%of the nitrogen available in ferrous ferricyanide. When the metalanalyzes 0.03% nitrogen, approximately 55 pounds of thenitrogen-containing material are required to increase the amount ofnitrogen in the melt to 0.06%. Thus, ferrous ferricyanide is highlyeffective in use. It is very economical to employ for it is cheap toprocure and can be used in small quantities with good results.

While my invention is directed particularly to using ferrousferricyanide as a nitrogen-introducing material in the production ofstainless steel, nitrogen also may be introduced into ferrochrome duringits production, this preferably being added to the melt during thereducing period. Also, in the production of stainless steel. There areother alternative materials which I propose to use in lieu of ferrousferricyanide. Copper cyanide, for example, can be employed in powderedor briquetted form for introducing nitrogen into a stainless steel whichcontains copper as an alloying element. Further, the use of othercyanides and ferricyanides of such metals as the alkali metals,particularly sodium and potassium, fall within the scope of the presentinvention.

Further, the non-corrosive ferrous alloys upon which my invention ispracticed, in consequence, are much improved in quality. A uniformdistribution of nitrogen is obtained throughout the metal. The nitrogen,therefore, imparts a more uniform and even grain structure and aconsistently finer grain structure to the metal. The finished alloy isfree from impurities and no trace of metal foreign to the desiredelements in the 6 alloy is present. Such metals are strong and durablethroughout and are free from gas flaws and other defects.

Thus it will be seen that in the present invention, a new process forintroducing nitrogen into stainless steel is provided, by the use ofwhich the various objects hereinbefore noted, along with many thoroughlypractical advantages, are successfully achieved. It will be observedthat the physical properties of rustless ferrous alloys are greatlyimproved by the practice of my invention and that these improvements areachieved at great savings in manufacture heretofore unrealized; and thatthe useful field of application of these products has been broadenedboth from the standpoints of economy and improved quality.

As many possible embodiments may be made of my invention and as manychanges may be made in the einbodients hercinbefore set forth, it is tobe understood that ail matter described herein is to be interpreted asillustrative and not in a limiting sense.

I claim:

1. In the production of stainless steel of appreciable nitrogen content,the art which includes preparing a bath of stainless steel, and addingto said bath a briquetted material substantially comprisingferro-chromium and copper cyanide.

2. In manufactures of the class described, a briquettednitrogen-treating agent comprising a substantial amount of coppercyanide and ferrochromium.

3. In the production of stainless steel of appreciable nitrogen content,the art which includes preparing a bath of stainless steel, and addingto said bath a briquetted material substantially comprisingferro-chromium and at least one cyanide of the group consisting ofcyanides of sodium, potassium and copper.

ALEXANDER L. FEED.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,471,252 Falvet Oct. 16, 19231,990,589 Franks Feb. 12, 1935 2,098,567 Comstock et al. Nov. 9, 19372,121,055 Smith et al June 23, 1938 2,174,740 Graham et al. Oct. 3, 19392,378,397 Feild June 19, 1945

